1. Field of the Invention
The present invention relates to video signal processing; more particularly, the present invention relates to decoders and methods for separating luminance and chrominance information from a composite video signal.
2. Descriptions of the Related Art
Video, a technology which is first developed for TV systems, processes a sequence of still images and represent them in motion. Video has been further developed in various formats to allow different media, such as internet or disks, for storage and distribution.
A composite video signal is composed of luminance and chrominance components, wherein luminance is a photometric measure of the density of luminous intensity and chrominance is used to represent the color information of the pictures. For example, a luminance component of a TV video signal carries the primary gray-level information and is suitable for display in a monochrome TV, and the chrominance component carries color information of the TV video signal and is mixed with the luminance component to generate an RGB signal for TV display.
More specifically, the TV video signal can be a NTSC color television signal which includes a luminance component ranging in frequency from direct current to a nominal bandwidth of 4.2 MHz, and a 3.58 MHz subcarrier which is modulated in phase and amplitude to represent hue and saturation of the image. Typically, the subcarrier is demodulated to produce color difference signals which are combined with the luminance component for reproduction of red, blue, and green color information. As is well known, simple filters have long been used to separate the chrominance from the luminance in television receivers. In particular, the composite video signal is typically fed to a low pass filter to extract the luminance information, and to a band pass filter to extract the chrominance information.
However, cross luminance artifacts, such as hanging dots and sot crawls, usually appear after separating chrominance and luminance from the composite video signal because of the cross luminance and cross chrominance (cross color). In summary, because video display quality is important to viewers, a method of luminance and chrominance separation without producing cross luminance artifacts is desirable.